Cost to heater water tank with gas boiler?

Jibber123

I just got back from a week holiday and read the meter before we left and when we got back, to see how much energy we used when the house was empty electricity was about 6.5kWh per day so 270watts per hour which is reasonable I guess. water and gass both zero as everything was off. I then flicked the hot water on for 1 hour using the extra hour button on the controller, so we could shower etc and after about 55min the boiler shut down as the tank was up to temp about 60C. I then checked the gas meter again and the boiler had used 8.5kWh of gas (0.27cu ft) Assuming it was at ambient temp room temp in the house when we got back which was 12C, and the tank volume is 140l as per the label on the tank. Q=m * cp * dt .I get 7.8kWh needed so the boiler and associated pipework is 92% efficient and costs about 87p. Does this sound about right?

k_man

Gas usage sounds about right.

I would however be more concerned about the electricity.
6.5kWh per day is around what many households use when occupied.
Your 6.5kWh when empty, equates to 2400kWh per year just on background usage.

The (albeit not representative) quoted typical household usage, that the yearly price cap figures are based on is 2900kWh

eastcorkram

6.5 kWh per day is pretty much spot on for our use (when we are NOT on holiday). We do both work full time though. 

[Deleted User]

Gas is inefficient in a number of ways. Firstly, there is the efficiency of the boiler: testing shows that condensing boilers rarely condense when re-heating cylinders. Secondly, there is the piping to take into consideration. Unless these pipes are fully lagged, they are effectively a mini radiator. Thirdly, a boiler doesn’t suddenly reach its set temperature: until the temperature in the water coil equals that of the water around it, the coil will extract heat from the cylinder.

We have PV solar. On Friday when the sun was shining, it took 3.9kWh of electricity to re-heat our cylinder to its set temperature. On Saturday, when the sun didn’t shine, it took 8.3kWh of gas. The two tank thermostats are set to same temperature. 

Alnat1

Usual suspects are American fridge freezers more than around 5 years old which are often found to be using 3kWh/day, fish tanks with heaters and pond pumps. Security lighting that gets triggered a lot and isn't LED can use a surprising amount, especially if it's on for 5 minutes each time. 

Various appliances in standby/not switched off at the plug can use a small amount of electricity, if you have a lot of these type of things they do start to add up. TVs/Sky type boxes which are internet connected and update, sound systems, PCs, microwave, cooker, washer, tumble dryer, dishwasher, toaster, touch lamps, etc.

Jibber123

ok so all that was left on was a couple of PIR led security flood lights 15w each but both work on PIRS so should only come on for a few minuets if triggered. The virgin media hub broadband box. A 4 years old fridge freezer in he kitchen and a 2 year old full height fridge 3 year old full height freezer in the garage. the cooker (just the clock). All tv's and other stuff, printers, computers etc were switched off at the plug. There is a car battery trickle charger on in the garage as well but it only comes on for a few minuets a day to top up a battery.

Alnat1

You could buy an energy monitor and test everything that plugs into a socket to try and find any vampire devices or appliances that are using more than you'd expect. There seems to be a mystery SOMETHING guzzling your electricity.

Forum favourite is a Tapo P110, about £10 from various retailers.